The commercialisation of geolocation systems such as GPS has led to a proliferation of portable, and in many cases hand-held, commercially available geolocation devices including GPS tracking devices. These are typically battery powered and therefore exhibit a limited operational lifetime between battery charges or replacement.
Such devices operate by repeatedly listening for the timing signals emitted by a network of satellites having known orbits. The position of such devices is identified by a process of determining the device's location relative to several (typically three or four) such satellites whereby the position of the geolocation device may be determined.
Such geolocation devices repeatedly go through a listening cycle, during which they try to acquire timing signals from multiple satellites within a field of view. Once sufficient signals have been acquired, a calculation may be made of the device's position, based on those received signals and data obtained either from the signals themselves or from another source, and the calculated position either displayed to a user or otherwise conveyed to an associated device which can use the positional information, including transmitting the information over an uplink (for example via a GPRS or GSM link) to a remote device or system. Conversely device control, configuration, and other information may be transmitted over a downlink from the remote device or system to the geolocation device.
In order to vary the useful period during which such devices may be operated on a single battery charge it is known to vary the delay between listening cycles: the longer the interval the less power is used over an extended period. Current systems are know to vary the time interval between listening periods and this can be user controlled.
Despite such methods, battery life remains an issue with such devices and it is therefore desirable to develop alternative and improved methods of conserving battery life for these and other similar devices, whilst at the same time providing useful positioning data.